This invention relates to mold clamping devices used for sealing semiconductor elements with resin.
FIG. 4 is a side view of a conventional mold clamping device. An upper metallic mold 31 secured to an upper platen 32 opposes a lower metallic mold 34 secured to a movable plated 33. The movable platen 33 is slidably supported on tie-bars 36a and 36b, which are fixed to the upper platen 32 and the lower platen 35 by means of the tie-bar fixing nuts 39a through 39h. A driving mechanism 37 drives a ball thread 38 via a gear train 40 and a ball thread support 41 accommodated within the lower platen 35, and thereby vertically translates the movable platen 33 slidably supported on the tie bars 36a and 36b. 
The operation of the mold clamping device of FIG. 4 is as follows. The ball thread 38 is driven and rotated by the driving mechanism 37 through the gear train 40 and the ball thread support 41, thereby lifting the movable platen 33 and the lower metallic mold 34. After the lower metallic mold 34 contacts upon the upper metallic mold 31, the tie-bars 36a and 36b are extended by the force exerted from the lower metallic mold 34. The lower metallic mold 34 is stopped at a position where a predetermined clamping force is developed between the upper metallic mold 31 and the lower metallic mold 34.
Then, the semiconductor element accommodated within the cavity formed between the upper metallic mold 31 and the lower metallic mold 34 is sealed with resin. After the resin sealing is completed, the ball thread 38 is rotated in the reverse direction, such that the movable platen 33 and the lower metallic mold 34 are lowered to the original position.
The above conventional mold clamping device, however, suffers the following disadvantage. During the clamping operation the reaction from the upper metallic mold 31 of the clamping force acting on the lower metallic mold 34 is concentrated at the ball thread support 41, and, as a result, the ball thread support is prone to fail.
It is therefore an object of this invention to provide a mold clamping device by which the reaction of the clamping force from the upper metallic mold 31 acting on the transmission mechanism may be dispersed, and hence the occurrences of failures are reduced and the reliability of the device is enhanced.
A further object of this invention is to provide a mold clamping device by which the clamping force can be measured accurately and the mold face bearing between the upper and the lower metallic molds (i.e., the distribution of the contact pressure between the contacting faces of the upper and lower metallic molds) can be adjusted easily.
The first object is accomplished in accordance with the principle of this invention by a mold clamping device for sealing a semiconductor element with a resin, which comprises a support base; a middle platen fixedly supported by the support base; a lower metallic mold fixedly secured upon an upper surface of the middle platen; a plurality of tie-bars vertically extending through and slidably supported by the middle platen; a movable platen fixedly secured to top end portions of the tie-bars; an upper metallic mold fixedly secured upon a lower surface of the movable platen to oppose the lower metallic mold, the lower metallic mold and the upper metallic mold defining a cavity for accommodating a semiconductor element during a resin molding and sealing process; a horizontal connecting bar member connecting lower ends of at least two of the tie-bars; a quadrilateral linkage mechanism having a form of a collapsible rhombus lying on a vertical plane, the rhombus exhibiting two vertices lying on a vertical line and the other two vertices lying on a horizontal line, wherein a top and a bottom vertex of the rhombus lying on the vertical line are rotatably coupled to the middle platen and the horizontal connecting bar member, respectively; a first and a second annular link rotatably coupled to the two vertices of the rhombus of the quadrilateral linkage mechanism, respectively, the first and a second annular link each having an inner thread formed on an inner surface thereof; a rod-shaped threaded member having a left handed first thread and a right-handed second outer thread formed at an outer side surface thereof, the first and second threads engaging with the inner thread of the first and second annular links, respectively, whereby a rotation of the rod-shaped threaded member in a first direction drives the annular links toward each other upon the rod-shaped threaded member, and a rotation of the rod-shaped threaded member in a second direction opposite to the first direction drives the annular links away from each other upon the rod-shaped threaded member; and a driving means for driving the rod-shaped threaded member selectively in the first and second direction, thereby lowering the upper metallic mold toward the lower metallic mold and raising the upper metallic mold away from the lower metallic mold, respectively, a driving force being transmitted from the driving means to the upper metallic mold through the rod-shaped threaded member, the annular links, the quadrilateral linkage mechanism, the horizontal connecting bar member, the tie-bars, and the movable platen.
Preferably, the annular links engage with the rod-shaped threaded member via ball threads formed upon the outer side surface thereof.
The second object is accomplished by the provision of: linear scales disposed near and parallel to the tie-bars, wherein elongations of the tie-bars indicative of clamping forces upon contact of the lower metallic mold with the upper metallic mold are measured by means of the linear scales. Further, the second object is accomplished by the provision of: a first and a second tie-bar fixing nut engaging with an upper end portion of a first and a second of the tie-bars, respectively, and supporting the movable platen at respective vertical levels, wherein the respective vertical levels of the movable platen are adjusted by turning the tie-bar fixing nuts; a first and a second pulley fixedly secured to the first and second tie-bars, respectively, the first and second pulleys having distinct numbers of teeth formed on outer side surfaces thereof; and timing belt span on the first and second pulleys, the timing belt having teeth formed upon an inner surface thereof engaging with the teeth formed on outer side surfaces of the first and second pulleys, such that the first and second pulleys are turned together by means of the timing belt, to adjust a tilting of the movable platen, thereby adjusting a mold face bearing between the lower metallic mold and the upper metallic mold.